1. Field of the Invention
This invention relates to vacuum filters for separating solid particles from gaseous materials which contain or consist of condensable substances, and in particular to a vacuum filter for separating dust from vapours, which filter contains at least one filter tube in a housing, the gaseous material which is to be filtered flowing through the wall of the filter tube so that the solid substances which are required to be separated are retained by the wall of the tube.
2. Description of the Prior Art
One of the problems in filters of this kind and in particular in vacuum filters connected to containers which are at a reduced pressure is that the temperature of the gaseous material which is required to be filtered must not drop below the dew point of the vapour during the filtration process because otherwise the vapour would at least partly condense on the filter. Some vapour is thereby lost and the filtering action is impaired.
In known vacuum filters, it is attempted to overcome this problem by passing the vapour at a sufficiently high temperature through the filter so that it will not cool below its dew point. This, however, requires the vapour to be raised to high temperatures, which in turn entails a high consumption of energy and in any case such high temperatures are not always possible in practice. The problem is not adequately solved by thermally insulating the filter to prevent external heat loss by radiation.